A conventional planetary gear reduction system has a sun gear having external teeth, a plurality of planet gears each having external teeth in meshing engagement with the external teeth of the sun gear, a common planet carrier supporting journal shafts of the planet gears for establishing relative positions of the planet gears, and a ring gear having internal teeth in meshing engagement with external teeth of the planet gears. With the arrangement, the drive force generated at the drive source such as a gas turbine engine is transmitted to the sun gear and then to the planet gears. The drive force transmitted to the planet gears are outputted in two different ways, for example, in the form of rotational force of the ring gear which is caused by the rotational motions of the planet gears and in the form of another rotational force of the planet carrier which is caused by orbital motions of the planet gears relative to the sun gear. See U.S. Pat. No. 5,466,198, for example.
In operation of the aircraft equipped with the planetary gear reduction system, the journal shafts of the planet gears tend to deflect or skew circumferentially due to torque forces applied to the planet carrier. This may cause the journal shafts of the planet gears out of parallel to the axis of the sun gear, which in turn results in that the planet gears make improper engagements with the sun gear and the ring gear and the journals of the planet gears become unevenly supported by their bearings. Eventually, the life of the planetary gear reduction system is reduced.
Therefore, it is an object of the present invention to provide a planetary gear reduction system which is capable of effectively restricting or minimizing the deflections of the journal shafts of the planet gears and thereby extending a life span of the system.